Reset your data isn't necessary. For example I don't want to reset my well-learned and strong team just to get the sigil.
All you have to do is play leagues/tournaments, win all 4 Wakka OD-s. The last one, Aurochs Reels will be a tournament prize. If you playing a league while getting the Aurochs Reels, then play the league through, and after the last match (the 10th), go out, SAVE, go back to blitzball menu and see the prize of the league. If it isn't the Jupiter Sigil, just soft reset the game (L1+L2+R1+R2+Select+Start), load, then go back.
Important: DO NOT ENTER the league if the prize is not the sigil, use soft reset immediately. The prize will changes if you won't enter the league. Soft reset until Jupiter Sigil will be the prize. That's all, hope I helped.